Substrate structures for integrated series connected photovoltaic arrays and process of manufacture of such arrays

ABSTRACT

This invention comprises manufacture of photovoltaic cells by deposition of thin film photovoltaic junctions on metal foil substrates. The photovoltaic junctions may be heat treated if appropriate following deposition in a continuous fashion without deterioration of the metal support structure. In a separate operation, an interconnection substrate structure is provided, optionally in a continuous fashion. Multiple photovoltaic cells are then laminated to the interconnection substrate structure and conductive joining methods are employed to complete the array. In this way the interconnection substrate structure can be uniquely formulated from polymer-based materials employing optimal processing unique to polymeric materials. Furthermore, the photovoltaic junction and its metal foil support can be produced in bulk without the need to use the expensive and intricate material removal operations currently taught in the art to achieve series interconnections.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of U.S. patent applicationSer. No. 12/154,078 filed May 19, 2008 now U.S. Pat. No. 7,732,243entitled Substrate Structures for Integrated Series ConnectedPhotovoltaic Arrays and Process of Manufacture of Such Arrays, which isa Continuation-in-Part of U.S. patent application Ser. No. 10/600,287filed Jun. 21, 2003, now abandoned entitled Methods and Structures forProduction of Selectively Electroplated Articles, now abandoned, whichis a Continuation-in-Part of U.S. patent application Ser. No. 10/144,901filed May 13, 2002, now abandoned entitled Methods and Structures forProduction of Selectively Electroplated Articles, now abandoned, whichis a Continuation-in-Part of U.S. patent application Ser. No. 09/498,102filed Feb. 4, 2000, entitled Substrate Structures for Integrated SeriesConnected Photovoltaic Arrays and Process of Manufacture of Such Arrays,and now U.S. Pat. No. 6,459,032. The entire contents of the aboveidentified applications are incorporated herein by this reference.

BACKGROUND OF THE INVENTION

Photovoltaic cells have developed according to two distinct methods. Afirst form produces cells employing a matrix of crystalline siliconappropriately doped to produce a planar p-n junction. An intrinsicelectric field established at the p-n junction produces a voltage bydirecting solar photon produced holes and free electrons in oppositedirections. Good conversion efficiencies and long-term reliability havebeen demonstrated for crystalline silicon cells. However, widespreadenergy collection using crystalline silicon cells is thwarted by thehigh cost of crystal silicon (especially single crystal silicon)material and interconnection processing.

A second approach to produce photovoltaic cells is by depositing thinphotovoltaic semiconductor films on a supporting substrate. Many varioustechniques have been proposed for deposition of semiconductor thinfilms. The deposition methods include vacuum vapor deposition, vacuumsputtering, electroplating, chemical vapor deposition and printing ofnanoparticle inks. These structures have become know in the art as “thinfilm” devices. Material requirements are minimized and technologies canbe proposed for mass production. Typical semiconductors used for thinfilm photovoltaic devices include cuprous sulfide, cadmium telluride(CdTe), copper-indium-gallium-diselenide (CIGS), amorphous silicon,printed silicon, and dye sensitized polymeric materials. The thin filmstructures can be designed according to doped homojunction technology orcan employ heterojunction approaches such as those using CdTe orchalcopyrite materials.

Despite significant improvements in individual cell conversionefficiencies for both single crystal and thin film approaches,photovoltaic energy collection has been generally restricted toapplications having relatively low power requirements. One factorimpeding development of bulk power systems is the problem ofeconomically collecting the energy from an extensive collection surface.Photovoltaic cells can be described as high current, low voltagedevices. Typically individual cell voltage is less than about two volts,and often less than 0.6 volt. The current component is a substantialcharacteristic of the power generated. Efficient energy collection froman expansive surface must minimize resistive losses associated with thehigh current characteristic. A way to minimize resistive losses is toreduce the size of individual cells and connect them in series. Thus,voltage is stepped through each cell while current and associatedresistive losses are minimized.

Regardless of whether the cells are crystalline silicon or thin film,making effective, durable series connections among multiple small cellscan be laborious, difficult and expensive. In order to approacheconomical mass production of series connected arrays of individualcells, a number of factors must be considered in addition to the type ofphotovoltaic materials chosen. These include the substrate employed andthe process envisioned. A first problem which has confronted productionof expansive surface photovoltaic modules is that of collecting thephotogenerated current from the top, light incident surface. Transparentconductive oxide (TCO) layers are normally employed to form a topsurface. However, these TCO layers are relatively resistive compared topure metals. Thus, efforts must be made to minimize resistive losses intransport of current through the TCO layer. One approach is simply toreduce the surface area of individual cells to a manageable amount.However, as cell widths decrease, the width of the area betweenindividual cells (interconnect area) should also decrease so that therelative portion of inactive surface of the interconnect area does notbecome excessive. Typical cell widths of one centimeter or less areoften taught in the art. These small cell widths demand very fineinterconnect area widths, which dictate delicate and sensitivetechniques to be used to electrically connect the top TCO surface of onecell to the bottom electrode of an adjacent series connected cell.Furthermore, achieving good stable ohmic contact to the TCO cell surfacehas proven difficult, especially when one employs those sensitivetechniques available when using the TCO only as the top collectorelectrode.

One approach to expand the surface area of individual cells whileavoiding excessive resistive losses in current collection is to form acurrent collector grid over the surface. This approach positions highlyconductive material in contact with the surface of the TCO in a spacedarrangement such that the travel distance of current through the TCO isreduced. In the case of the classic single crystal silicon orpolycrystal silicon cells, a common approach is to form a collector gridpattern of traces using a silver containing paste and then fuse thepaste to sinter the silver particles into continuous conductive silverpaths. These highly conductive traces normally lead to a collection busssuch as a copper foil strip. One notes that this approach involves useof expensive silver and requires the photovoltaic semiconductors totolerate the high fusion temperatures. The sintering temperaturesinvolved are normally unsuitable for thin film photovoltaic structures.Another approach is to attach an array of fine copper wires to thesurface of the TCO. The wires may also lead to a collection buss, oralternatively extend to an electrode of an adjacent cell. This wireapproach requires positioning and fixing of multiple fine fragile wireswhich makes mass production difficult and expensive. Another approachcommonly used for thin film photovoltaic cells is to print a collectorgrid array on the surface of the TCO using a conductive ink, usually onecontaining a heavy loading of fine particulate silver. The ink is simplydried or cured at mild temperatures to remove a solvent carrier.Compared to the high sintering temperatures associated with the silverpastes employed with crystal silicon cells, the milder curingtemperatures for silver inks typically do not adversely affect thin filmphotovoltaic structures. However, the silver ink approaches require theuse of relatively expensive inks because of the required high loading offinely divided silver. Furthermore, batch printing on the individualcells is laborious and expensive.

In addition to current collection from the top surface of cells,efficient photovoltaic power collection includes integration of multiplecells into arrays or modules to create a desired surface area. Themultiple cells are typically electrically integrated in seriesarrangement such that the power is accumulated in voltage increments.Regarding crystalline silicon cells, the individual cells are normallyinitially discrete and comprise rigid wafers approximately 200micrometers thick and approximately 230 square centimeters in area. Aconventional way to harvest power from multiple such cells is to use aconventional “string and tab” arrangement. This technique involves firstdepositing fine conductive current collecting grid fingers over thelight incident surface. As previously discussed, these fingers often arein the form of a fired silver paste or fine metal wires. Multiple gridfingers lead to a robust buss of substantial current carrying capacity.This buss material then extends and is electrically joined to the bottomelectrode of an adjacent cell. Such methods for electrically integratingmultiple discrete cells can be termed “discrete integration”.

A typical prior art “string and tab” arrangement for achieving seriesconnections among crystalline silicon cells is embodied in FIGS. 1Athrough 1C. It is in seen in FIG. 1A that conductive grid fingers 82 areattached to the light incident (top) surface 83 of cells 84. Thesefingers 82 extend to buss material 85 positioned at opposite peripheraledges of cells 84. The buss material extends to the bottom electrode 86of an adjacent cell, as is shown in the bottom view of FIG. 1B and sideview of FIG. 1C. It is to be noted that the busses 85 in FIGS. 1Athrough 1C are depicted with section lines. This is done for contrastonly and the views are not actually sectional views. While FIGS. 1Athrough 1C show the interconnection of two cells, in reality thisconnection is normally made among strings of many more cells (8 forexample). This process is thus laborious, costly and subject tomanufacturing error. Further, the strings of cells are physically turnedover in order to access both top and bottom surfaces of the individualcells to accomplish the electrical connections. Such a process may leadto breaking of electrical connections and complicates efforts to achievea continuous high volume production process for the integrated cells.

Thin film photovoltaic semiconductors can be deposited over expansiveareas and often in a continuous roll-to-roll fashion. Thin filmtechnologies may thus offer additional opportunities for mass productionof interconnected arrays compared to inherently small, discrete singlecrystal silicon cells. For example, thin film photovoltaic cells may besubdivided and interconnected into arrays of multiple cells using aprocess generally referred to as “monolithic integration”. Monolithicintegration envisions initially depositing photovoltaic cell structureover an expanded surface of supporting substrate. The expansivephotovoltaic structure is subsequently subdivided into smaller,isolated, individual cells which are then serially interconnected whilemaintaining the cells on the initial common substrate.

A number of U.S. patents have issued proposing designs and processes toachieve such monolithic series integration among thin film photovoltaiccells. Examples of these proposed processes are presented in U.S. Pat.Nos. 4,443,651, 4,724,011, and 4,769,086 to Swartz, Turner et al. andTanner et al. respectively which taught monolithic integrationtechniques for photovoltaic cells supported by glass substrates. Theprocess comprises deposition of photovoltaic materials on glasssubstrates followed by scribing to form smaller area individual cells.Multiple steps then follow to electrically connect the individual cellsin series array. While expanding the opportunities for mass productionof interconnected cell arrays compared with single crystal siliconapproaches, glass substrates must inherently be processed on anindividual batch basis. Further, when multiple individual cells areformed monolithically on a common monolithic glass substrate, there isno way to check the quality of individual cells and remove deficientcell regions. Thus variations in cell quality over an expansive surfacemay jeopardize the entire module.

More recently, developers have explored depositing wide area films usingcontinuous roll-to-roll processing. This technology generally involvesdepositing thin films of photovoltaic material onto a continuouslymoving sheetlike web of insulating plastic or metal foil. However, achallenge still remains regarding monolithically subdividing theexpansive films into individual cells followed by interconnecting into aseries connected array. For example, U.S. Pat. No. 4,965,655 to Grimmeret. al. and U.S. Pat. No. 4,697,041 to Okinawa teach processes employinginsulating polymeric substrates requiring expensive laser scribing andinterconnections achieved with laser heat staking. In addition, thesetwo references teach a substrate of thin vacuum deposited metal onsubstrate films of relatively expensive polymers. The electricalresistance of thin vacuum metallized layers may significantly limit theactive area of the individual interconnected cells. Finally, whenmultiple individual cells are formed on a common monolithic polymersupport film it is difficult to check the quality of individual cellsand remove deficient cell regions. Thus variations in cell quality overan expansive surface may jeopardize the entire module.

It has become well known in the art that the efficiencies of certainpromising thin film photovoltaic junctions such as those based oncopper-indium-gallium-diselenide or cadmium telluride can besubstantially increased by high temperature treatments. These treatmentsinvolve temperatures at which even the most heat resistant and expensiveplastics suffer rapid deterioration. Therefore, from a practicalstandpoint these thin film photovoltaic semiconductors are most oftendeposited on ceramic, glass, or metal substrates to support the thinfilm junctions. Use of a glass or ceramic substrates generally restrictsone to batch processing and handling difficulty. Use of a metal foil,such as stainless steel, as a substrate allows continuous roll-to-rollmanufacture of cell structure over an expansive surface. However,despite the fact that use of a metal foil allows high temperatureprocessing in roll-to-roll fashion, the subsequent interconnection ofindividual cells effectively into an interconnected array has provendifficult, in part because the metal foil substrate is electricallyconducting. For example, the monolithic integration techniques possiblewith insulating substrates are not possible using metal foil substrates,since the common substrate is a conducting metal and would not permitthe required electrical isolation of individual cells prior toelectrical series interconnection.

Many manufacturers of thin film photovoltaic devices supported on metalfoil substrates choose to subdivide the material into discrete cellsprior to assembly into an interconnected array. Typical of these methodsis that which replicates the “string and tab” legacy approaches used formodule assembly of crystalline silicon cells. Here the expansive metalfoil/photovoltaic structure is subdivided into individual cells,typically of dimensions about 15 cm. by 15. cm, before subsequentassembly via the “string and tab” approach described above.

Some attempts have been advanced to achieve the advantages of continuousproduction of interconnected modules using continuously produced cellstructure supported on a metal foil substrate. U.S. Pat. No. 4,746,618to Nath et al. teaches a design and process to achieve interconnectedarrays using roll-to-roll processing of a metal web substrate such asstainless steel. U.S. Pat. No. 4,746,618 is hereby incorporated in itsentirety by reference. The process includes multiple operations ofcutting, selective deposition, material removal and riveting. Theseoperations add considerably to the final interconnected array cost. U.S.Pat. No. 5,385,848 to Grimmer teaches roll-to-roll methods to achieveintegrated series connections of adjacent thin film photovoltaic cellssupported on an electrically conductive metal substrate. U.S. Pat. No.5,385,848 is hereby incorporated in its entirety by reference. Theprocess includes mechanical or chemical etch removal of a portion of thephotovoltaic semiconductor and transparent top electrode to expose anupper surface portion of the electrically conductive metal substrate.The exposed metal serves as a contact area for interconnecting adjacentcells. These material removal techniques are troublesome for a number ofreasons. First, many of the chemical elements involved in the bestphotovoltaic semiconductors are expensive and environmentallyunfriendly. This removal subsequent to controlled deposition involvescontainment, dust and dirt collection and disposal, and possible cellcontamination. This is not only wasteful but considerably adds toexpense since a significant amount of the valuable photovoltaicsemiconductor is lost to the removal process. Ultimate moduleefficiencies are further compromised in that the spacing betweenadjacent cells grows, thereby reducing the effective active collectorarea for a given module area.

Yet another approach to achieve current collection and seriesinterconnections among multiple cells while maintaining the flexiblecharacteristic of many thin film structures is represented by theteachings of Yoshida et al. in U.S. Pat. No. 5,421,908. U.S. Pat. No.5,421,908 is hereby incorporated in its entirety by reference. Anembodiment of the current collection teachings of Yoshida et al. ispresented in FIGS. 2A through 2C. Yoshida et al. teach a process whereina conductive rear “1^(st)” electrode 94 is first deposited using vacuumprocessing onto a polymeric film 96 as shown in FIG. 2A. Through holes92 are then formed through the laminate. As shown in FIG. 2B, anoverlaying amorphous silicon photovoltaic film 97 and TCO “2^(nd)”electrode layer 98 are deposited on the laminate and through the holes.As shown in FIG. 2C, electrical communication between a top surface TCO“2^(nd)” electrode 98 and a backside “3^(rd)” electrode 99 is madethrough the holes when the “3^(rd)” electrode 99 is deposited on therear of the structure, as shown in FIG. 2C. The rear “3^(rd)” electrode99 is deposited by vacuum processing which also may coat the side wallsof the holes. As Yoshida et al. teach, the “2^(nd)” and “3^(rd)”electrode layers in the holes are insulated from the “1^(St)” electrode94 by the high resistance of the amorphous silicon semiconductor layer.One readily realizes that an appropriate insulating layer would have tocoat the holes to separate these electrodes should a semiconductor oflower resistivity be employed. To complete a series connection to anadjacent cell, the “3^(rd)” electrode 99 of a first cell is furtherelectrically joined to rear “1^(st)” electrode 94 of an adjacent cellthrough additional holes between scribe lines separating the adjoiningcells.

The through holes taught by Yoshida represent means to transport currentfrom the topside surface of a photovoltaic cell to a conductive material(“3^(rd)” electrode) located remote from the top surface. Thus thethrough holes of Yoshida et al. are functionally equivalent to thesilver grid lines and wire forms discussed above in relation to FIGS. 1Athrough 1C.

A number of manufacturing and performance problems are intrinsic withthe method and structure taught by Yoshida et al. First, both the“1^(st)” rear cell electrode and the “3^(rd)” backside electrode arerelatively thin, being formed by vacuum sputtering. Vacuum processing isexpensive and in practice yields relatively thin deposits. As taught byYoshida et al. deposits of less than one half micrometer were employed.This relatively low practical thickness limits the current carryingability of the deposited metal and thereby restricts the size of theindividual cells. Moreover, absent additional conductive fill materialin the holes, the connection between the backside “3^(rd)” electrode andthe rear “1^(st)” electrode of adjacent cells is achieved only through avery restricted cross section. This is a result of the limited access tothe “1^(st)” electrode, since there is no access to the broad surfaceregions of the “1^(st)” electrode, only its edge surface. The primarysupport for the Yoshida structure is the insulating polymeric film,which thus must be present during formation of the semiconductors. Whileperhaps acceptable when manufacturing amorphous silicon cells taught byYoshida et al., it may be unlikely that the films taught would besuitable for the heat treatment requirements of other notable thin filmsemiconductors. The hole density taught by Yoshida et al. is quite large(15 mm centers) adding to complexity. However, even with the large holedensity, the resistive losses expected in current transport to the holeswould be quite large given the sheet resistance of a normal TCO. Toaddress this issue, Yoshida et al. proposed a structure combiningprinted silver ink grid lines leading to a reduced number of throughholes (see for example FIG. 28A of U.S. Pat. No. 5,421,908). Finally,many individual cells are formed on a common monolithic support filmusing the Yoshida et al. teaching. There is no way to check the qualityof individual cells and remove deficient cell regions. Thus variationsin cell quality over an expansive surface jeopardize the entire module.

Thus there remains a need for manufacturing processes and articles whichallow facile production of photovoltaic semiconductor structures whilealso offering unique means to achieve effective integrated connectionsto result in final modular array.

In a somewhat removed segment of technology, a number of electricallyconductive fillers have been used to produce electrically conductivepolymeric materials. This technology generally involves mixing of aconductive filler such as silver particles with the polymer resin priorto fabrication of the material into its final shape. Many choices existfor the conductive filler, including those comprising metals such assilver, copper and nickel, those comprising conductive metal oxides suchas indium-tin oxide and zinc oxide, intrinsically conductive polymers,graphite, carbon black and the like. Conductive fillers may have highaspect ratio structure such as metal fibers such as stainless steelfibers or metallized polymer fibers. Other high aspect ratio materialssuch as metal flakes or powder, or highly structured carbon blacks maybe appropriate, with the choice based on a number of cost/performanceconsiderations. More recently, fine particles of intrinsicallyconductive polymers have been employed as conductive fillers within aresin binder. Electrically conductive polymers have been used as bulkthermoplastic compositions, or formulated into paints and inks. Theirdevelopment has been spurred in large part by electromagnetic radiationshielding and static discharge requirements for plastic components usedin the electronics industry. Other known applications include resistiveheating fibers and battery components and production of conductivepatterns and traces. The characterization “electrically conductivepolymer” covers a very wide range of intrinsic resistivities dependingon the filler, the filler loading and the methods of manufacture of thefiller/polymer blend. Resistivities for filled electrically conductivepolymers may be as low as 0.00001 ohm-cm. for very heavily filled silverinks, yet may be as high as 10,000 ohm-cm or even more for lightlyfilled carbon black materials or other “anti-static” materials.“Electrically conductive polymer” has become a broad industry term tocharacterize all such materials. In addition, it has been reported thatrecently developed intrinsically conducting polymers (absent conductivefiller) may exhibit resistivities comparable to conductive metals.

In yet another separate technological segment, coating plasticsubstrates with metal electrodeposits has been employed to achievedecorative effects on items such as knobs, cosmetic closures, faucets,and automotive trim. The normal conventional process actually combinestwo primary deposition technologies. The first is to deposit an adherentmetal coating using chemical (electroless) deposition to first coat thenonconductive plastic and thereby render its surface highly conductive.This electroless step is then followed by conventional electroplating.ABS (acrylonitrile-butadiene-styrene) plastic dominates as the substrateof choice for most applications because of a blend of mechanical andprocess properties and ability to be uniformly etched. The overallplating process comprises many steps. First, the plastic substrate ischemically etched to microscopically roughen the surface. This isfollowed by depositing an initial metal layer by chemical reduction(typically referred to as “electroless plating”). This initial metallayer is normally copper or nickel of thickness typically one-halfmicrometer. The object is then electroplated with metals such as brightnickel and chromium to achieve the desired thickness and decorativeeffects. The process is very sensitive to processing variables used tofabricate the plastic substrate, limiting applications to carefullyprepared parts and designs. In addition, the many steps employing harshchemicals make the process intrinsically costly and environmentallydifficult. Finally, the sensitivity of ABS plastic to liquidhydrocarbons has prevented certain applications. ABS and other suchpolymers have been referred to as “electroplateable” polymers or resins.This is a misnomer in the strict sense, since ABS (and othernonconductive polymers) are incapable of accepting an electrodepositdirectly and must be first metallized by other means before beingfinally coated with an electrodeposit. The conventional technology forelectroplating on plastic (etching, chemical reduction, electroplating)has been extensively documented and discussed in the public andcommercial literature. See, for example, Saubestre, Transactions of theInstitute of Metal Finishing, 1969, Vol. 47., or Arcilesi et al.,Products Finishing, March 1984.

Many attempts have been made to simplify the process of electroplatingon plastic substrates. Some involve special techniques to produce anelectrically conductive film on the surface. Typical examples of thisapproach are taught by U.S. Pat. No. 3,523,875 to Minklei, U.S. Pat. No.3,682,786 to Brown et. al., and U.S. Pat. No. 3,619,382 to Lupinski. Theelectrically conductive film produced was then electroplated. None ofthese attempts at simplification have achieved any recognizablecommercial application.

A number of proposals have been made to make the plastic itselfconductive enough to allow it to be electroplated directly therebyavoiding the “electroless plating” process. It is known that one way toproduce electrically conductive polymers is to incorporate conductive orsemiconductive fillers into a polymeric binder. Investigators haveattempted to produce electrically conductive polymers capable ofaccepting an electrodeposited metal coating by loading polymers withrelatively small conductive particulate fillers such as graphite, carbonblack, silver or nickel powder or flake or small metal coated forms suchas metal coated mica. When considering polymers rendered electricallyconductive by loading with electrically conductive fillers, it may beimportant to distinguish between “microscopic resistivity” and “bulk” ormacroscopic resistivity”. “Microscopic resistivity” refers to acharacteristic of a polymer/filler mix considered at a relatively smalllinear dimension of for example 1 micrometer or less. “Bulk” or“macroscopic resistivity” refers to a characteristic determined overlarger linear dimensions. To illustrate the difference between“microscopic” and “bulk, macroscopic” resistivities, one can consider apolymer loaded with conductive fibers at a fiber loading of 10 weightpercent. Such a material might show a low “bulk, macroscopic”resistivity when the measurement is made over a relatively largedistance. However, because of fiber separation (holes) such a compositemight not exhibit consistent “microscopic” resistivity. When producingan electrically conductive polymer intended to be electroplated, oneshould consider “microscopic resistivity” in order to achieve uniform,“hole-free” deposit coverage. Thus, it may be advantageous to considerconductive fillers comprising those that are relatively small, but withloadings sufficient to supply the required conductive contacting. Suchfillers include metals such as silver in the form of powders or flake,metal coated particles such as mica or spheres, particles comprisingconductive metal oxides such as indium-tin oxide and zinc oxide, fineparticles of intrinsically conductive polymers, graphite powder andconductive carbon black and the like. Heavy loadings of such filler maybe sufficient to reduce volume resistivity to a level whereelectroplating may be considered.

However, attempts to make an acceptable electroplateable polymer usingthe small conductive fillers alone encounter a number of barriers.First, the most conductive fine metal containing fillers such as silverare relatively expensive. The loadings required to achieve theparticle-to-particle proximity to achieve acceptable conductivityincreases the cost of the polymer/filler blend dramatically. The metalcontaining fillers are accompanied by further problems. They tend tocause deterioration of the mechanical properties and processingcharacteristics of many resins. This significantly limits options inresin selection. All polymer processing is best achieved by formulatingresins with processing characteristics specifically tailored to thespecific process (injection molding, extrusion, blow molding, printingetc.). A required heavy loading of metal filler severely restrictsability to manipulate processing properties in this way. A furtherproblem is that metal fillers can be abrasive to processing machineryand may require specialized screws, barrels, and the like.

Another major obstacle involved in the electroplating of electricallyconductive polymers is a consideration of adhesion between theelectrodeposited metal and polymeric substrate (metal/polymer adhesion).In most cases sufficient adhesion is required to prevent metal/polymerseparation during extended environmental and use cycles. Despite beingelectrically conductive, a simple metal-filled polymer offers no assuredbonding mechanism to produce adhesion of an electrodeposit since themetal filler particles may be encapsulated by the resin binder or oxide,often resulting in a resin-rich or oxide “skin”.

A number of methods to enhance electrodeposit adhesion to electricallyconductive polymers have been proposed. For example, etching of thesurface prior to plating can be considered. Etching can be achieved byimmersion in vigorous solutions such as chromic/sulfuric acid.Alternatively, or in addition, an etchable species can be incorporatedinto the conductive polymeric compound. The etchable species at exposedsurfaces is removed by immersion in an etchant prior to electroplating.Oxidizing surface treatments can also be considered to improvemetal/plastic adhesion. These include processes such as flame or plasmatreatments or immersion in oxidizing acids.

In the case of conductive polymers containing finely divided metal, onecan propose achieving direct metal-to-metal adhesion betweenelectrodeposit and filler. However, here the metal particle surface maybe shielded by an aforementioned resin or oxide “skin”. To overcome thiseffect, one could propose methods to remove the “skin”, exposing activemetal filler to bond to subsequently electrodeposited metal. For thereasons described above, electrically conductive polymers employingmetal fillers have not been widely used as bulk substrates forelectroplateable articles. Nevertheless, revived efforts and advanceshave been made recently to accomplish electroplating onto printedconductive patterns formed by silver filled inks and pastes. Inaddition, such metal containing polymers have found considerableapplications as inks or pastes in production of printed conductivetraces for electrical circuitry, antennas etc.

Another approach to impart adhesion between conductive resin substratesand electrodeposits is incorporation of an “adhesion promoter” at thesurface of the electrically conductive resin substrate. This approachwas taught by Chien et al. in U.S. Pat. No. 4,278,510 where maleicanhydride modified propylene polymers were taught as an adhesionpromoter. Luch, in U.S. Pat. No. 3,865,699 taught that certain sulfurbearing chemicals could function to improve adhesion of initiallyelectrodeposited Group VIII metals.

An additional obstacle confronting practical electroplating ontoelectrically conductive polymers is the initial “bridge” ofelectrodeposit onto the surface of the electrically conductive polymer.In electrodeposition, the substrate to be plated is often made cathodicthrough a pressure contact to a highly conductive member under cathodicpotential. However, if the contact resistance is excessive or thesubstrate is insufficiently conductive, the electrodeposit currentfavors the highly conductive member to the point where theelectrodeposit will not bridge to the substrate.

Moreover, a further problem is encountered even if specialized rackingor cathodic contact successfully achieves electrodeposit bridging to thesubstrate. Many of the electrically conductive polymers haveresistivities far higher than those of typical metal substrates. Also,many applications contemplate electroplating onto a thin printedconductive ink pattern of traces or “fingers”. The dry conductive inkthickness is typically less than 25 micrometer and often less than 6micrometer. The conductive polymeric pattern may be relatively limitedin the amount of electrodeposition current which it alone can convey.Thus, the conductive polymeric substrate pattern does not cover almostinstantly with electrodeposit as is typical with metallic substrates.Except for the most heavily loaded and highly conductive polymersubstrates, a large portion of the electrodeposition current must passback through the previously electrodeposited metal growing laterallyover the surface of the conductive plastic substrate. In a fashionsimilar to the bridging problem discussed above, the electrodepositioncurrent favors the electrodeposited metal and the lateral growth can beextremely slow and erratic. This restricts the size and “growth length”of the conductive ink pattern, increases plating costs, and can alsoresult in large non-uniformities in electrodeposit integrity andthickness over the pattern.

This lateral growth is dependent on the ability of the substrate toconvey current. Thus, the thickness and resistivity of a conductivepolymeric ink pattern can be defining factors in the ability to achievesatisfactory electrodeposit coverage rates. When dealing withselectively electroplated patterns long thin metal traces are oftendesired, deposited on a relatively thin electrically conductive polymersubstrate patterns. These factors of course often work against achievingthe desired result.

This coverage rate problem likely can be characterized by a continuum,being dependent on many factors such as the nature of the initiallyelectrodeposited metal, electroplating bath chemistry, the nature of thepolymeric binder and the resistivity of the electrically conductivepolymeric substrate. As a “rule of thumb”, the instant inventorestimates that coverage rate issue would demand attention if theresistivity of a bulk conductive polymeric substrate rose above about0.001 ohm-cm. Alternatively, as a “rule of thumb” appropriate forconductive thin film substrate patterns, coverage rate issues mayrequire attention if the substrate pattern to be plated has a surface“sheet” resistance of greater than about 0.05 ohm per square.

The least expensive (and least conductive) of the readily availableconductive fillers for plastics are carbon blacks. Attempts have beenmade to electroplate electrically conductive polymers using carbon blackloadings. Examples of this approach are the teachings of U.S. Pat. Nos.4,038,042, 3,865,699, and 4,278,510 to Adelman, Luch, and Chien et al.respectively.

Adelman taught incorporation of conductive carbon black into a polymericmatrix to achieve electrical conductivity required for electroplating.The substrate was pre-etched in chromic/sulfuric acid to achieveadhesion of the subsequently electroplated metal. A fundamental problemremaining unresolved by the Adelman teaching is the relatively highresistivity of carbon loaded polymers. The lowest “microscopicresistivity” generally achievable with carbon black loaded polymers isabout 1 ohm-cm. This is about five to six orders of magnitude higherthan typical electrodeposited metals such as copper or nickel. Thus, theelectrodeposit bridging and coverage rate problems described aboveremained unresolved by the Adelman teachings.

Luch in U.S. Pat. No. 3,865,699 and Chien et al. in U.S. Pat. No.4,278,510 also chose carbon black as a filler to provide an electricallyconductive surface for the polymeric compounds to be electroplated. TheLuch U.S. Pat. No. 3,865,699 and the Chien U.S. Pat. No. 4,278,510 arehereby incorporated in their entirety by this reference. However, theseinventors further taught inclusion of materials to increase the rate ofelectrodeposit coverage or the rate of metal deposition on the polymer.These materials can be described herein as “electrodeposit growth rateaccelerators” or “electrodeposit coverage rate accelerators”. Anelectrodeposit coverage rate accelerator is a material functioning toincrease the electrodeposition coverage rate over the surface of anelectrically conductive polymer independent of any incidental affect itmay have on the conductivity of an electrically conductive polymer. Inthe embodiments, examples and teachings of U.S. Pat. Nos. 3,865,699 and4,278,510, it was shown that certain sulfur bearing materials, includingelemental sulfur, can function as electrodeposit coverage or growth rateaccelerators to overcome problems in achieving electrodeposit coverageof electrically conductive polymeric surfaces having relatively highresistivity or thin electrically conductive polymeric substrates havinglimited current carrying capacity.

In addition to elemental sulfur, sulfur in the form of sulfur donorssuch as sulfur chloride, 2-mercapto-benzothiazole,N-cyclohexyle-2-benzothiaozole sulfonomide, dibutyl xanthogen disulfide,and tetramethyl thiuram disulfide or combinations of these and sulfurwere identified. Those skilled in the art will recognize that thesesulfur donors are the materials which have been used or have beenproposed for use as vulcanizing agents or accelerators. Since thepolymer-based compositions taught by Luch and Chien et al. could beelectroplated directly they could be accurately defined as directlyelectroplateable resins (DER). These directly electroplateable resins(DER) can be generally described as electrically conductive polymerswith the inclusion of a growth rate accelerator.

Specifically for the present invention, specification, and claims,directly electroplateable resins, (DER), are characterized by thefollowing features:

-   -   (a) presence of an electrically conductive polymer;    -   (b) presence of an electrodeposit coverage rate accelerator;    -   (c) presence of the electrically conductive polymer and the        electrodeposit coverage rate accelerator in the directly        electroplateable composition in cooperative amounts required to        achieve direct coverage of the composition with an        electrodeposited metal or metal-based alloy.

In his patents, Luch identified elastomers such as natural rubber,polychloroprene, butyl rubber, chlorinated butyl rubber, polybutadienerubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber etc. assuitable for the matrix polymer of a directly electroplateable resin.Other polymers identified by Luch as useful included polyvinyls,polyolefins, polystyrenes, polyamides, polyesters and polyurethanes.

When used alone, the minimum workable level of carbon black required toachieve “microscopic” electrical resistivities of less than 1000 ohm-cm.for a polymer/carbon black mix appears to be about 8 weight percentbased on the combined weight of polymer plus carbon black. The“microscopic” material resistivity generally is not reduced below about1 ohm-cm. by using conductive carbon black alone. This is several ordersof magnitude larger than typical metal resistivities.

It is understood that in addition to carbon blacks, other well known,highly conductive fillers can be considered in DER compositions.Examples include but are not limited to metallic fillers such as silverpowder or flake, metal coated forms such as metal coated mica or glassspheres, graphite powder and conductive metal oxides. In these cases themore highly conductive fillers can be used to augment or even replacethe conductive carbon black. Furthermore, one may consider usingintrinsically conductive polymers to supply the required conductivity.In this case, it may not be necessary to add conductive fillers to thepolymer.

The “bulk, macroscopic” resistivity of fine conductive particle filledpolymers can be further reduced by augmenting the filler with additionalhighly conductive, high aspect ratio forms such as metal containingfibers. This can be an important consideration in the success of certainapplications. Furthermore, one should realize that incorporation ofnon-conductive fillers may increase the “bulk, macroscopic” resistivityof conductive polymers loaded with finely divided conductive fillerswithout significantly altering the “microscopic resistivity” of theconductive polymer “matrix” encapsulating the non-conductive fillerparticles.

Regarding electrodeposit coverage rate accelerators, both Luch and Chienet al. in the above discussed U.S. patents demonstrated that sulfur andother sulfur bearing materials such as sulfur donors and vulcanizationaccelerators function as electrodeposit coverage rate accelerators whenusing an initial Group VIII metal electrodeposit “strike” layer. Thus,an electrodeposit coverage rate accelerator need not be electricallyconductive, but may be a material that is normally characterized as anon-conductor. The coverage rate accelerator need not appreciably affectthe conductivity of the polymeric substrate. As an aid in understandingthe function of an electrodeposit coverage rate accelerator thefollowing is offered:

-   -   a. A specific conductive polymeric structure is identified as        having insufficient current carrying capacity to be directly        electroplated in a practical manner.    -   b. A material is added to the conductive polymeric material        forming said structure. Said material addition may have        insignificant affect on the current carrying capacity of the        structure (i.e. it does not appreciably reduce resistivity or        increase thickness).    -   c. Nevertheless, inclusion of said material greatly increases        the speed at which an electrodeposited metal laterally covers        the electrically conductive surface.        It is contemplated that a coverage rate accelerator may be        present as an additive, as a species absorbed on a filler        surface, or even as a functional group attached to a polymer        chain. One or more growth rate accelerators may be present in a        directly electroplateable resin (DER) to achieve combined often        synergistic results.

A hypothetical example is an extended trace of conductive ink having adry thickness of two micrometer. Such inks typically comprise aconductive filler such as silver, nickel, copper, conductive carbon etc.The limited thickness of the ink may reduce the current carryingcapacity of this trace thus preventing direct electroplating in apractical manner. However, inclusion of an appropriate quantity of acoverage rate accelerator may allow the conductive trace to be directlyelectroplated in a practical manner.

One might expect that other Group 6A elements, such as oxygen, seleniumand tellurium, could function in a way similar to sulfur. In addition,other combinations of electrodeposited metals, such as copper andappropriate coverage rate accelerators may be identified. It isimportant to recognize that such an electrodeposit coverage rateaccelerator is important in order to achieve direct electrodeposition ina practical way onto polymeric substrates having low conductivity orvery thin electrically conductive polymeric substrates having restrictedcurrent carrying ability.

It has also been found that the inclusion of an electrodeposit coveragerate accelerator promotes electrodeposit bridging from a discretecathodic metal contact to a DER surface. This greatly reduces thebridging problems described above.

Due to multiple performance problems associated with their intended enduse, none of the attempts identified above to directly electroplateelectrically conductive polymers or plastics has ever achieved anyrecognizable commercial success. Nevertheless, the current inventor haspersisted in personal efforts to overcome certain performancedeficiencies associated with the initial DER technology. Along withthese efforts has come a recognition of unique and eminently suitableapplications employing the DER technology. Some examples of these uniqueapplications for electroplated articles include solar cell electricalcurrent collection grids, electrodes, electrical circuits, electricaltraces, circuit boards, antennas, capacitors, induction heaters,connectors, switches, resistors, inductors, batteries, fuel cells,coils, signal lines, power lines, radiation reflectors, coolers, diodes,transistors, piezoelectric elements, photovoltaic cells, emi shields,biosensors and sensors. One readily recognizes that the demand for suchfunctional applications for electroplated articles is relatively recentand has been particularly explosive during the past decade.

It is important to recognize a number of important characteristics ofdirectly electroplateable resins (DERs) which facilitate the currentinvention. One such characteristic of the DER technology is its abilityto employ polymer resins and formulations generally chosen inrecognition of the fabrication process envisioned and the intended enduse requirements. A very wide choice of polymer resins and blends,additives and fillers is available with the directly electroplateableresin (DER) technology. Functional combinations of polymers andadditives, such as curatives, stabilizers, and adhesion promoters can bewidely chosen. In order to provide clarity, examples of some suchfabrication processes are presented immediately below in subparagraphs 1through 9.

-   -   (1) Should it be desired to electroplate an ink, paint, coating,        or paste which may be printed or formed on a substrate, a good        film forming polymer, for example a soluble resin such as an        elastomer, can be chosen to fabricate a DER ink (paint, coating,        paste etc.). For example, in some embodiments thermoplastic        elastomers having an olefin base, a urethane base, a block        copolymer base or a random copolymer base may be appropriate. In        some embodiments the coating may comprise a water based latex.        Other embodiments may employ more rigid film forming polymers.        The DER ink composition can be tailored for a specific process        such flexographic printing, rotary silk screening, gravure        printing, flow coating, spraying etc. Furthermore, additives can        be employed to improve the adhesion of the DER ink to various        substrates. One example would be tackifiers.    -   (2) Very thin DER traces often associated with electrical traces        such as current collector grid structures can be printed and        then electroplated due to the inclusion of the electrodeposit        growth rate accelerator.    -   (3) Should it be desired to cure the DER substrate to a 3        dimensional matrix, an unsaturated elastomer or other “curable”        resin may be chosen.    -   (4) DER inks can be formulated to form electrical traces on a        variety of flexible substrates. For example, should it be        desired to form electrical structure on a laminating film, a DER        ink adherent to the sealing surface of the laminating film can        be effectively electroplated with metal and subsequently        laminated to a separate surface.    -   (5) Should it be desired to electroplate a fabric, a DER ink can        be used to coat all or a portion of the fabric intended to be        electroplated. Furthermore, since DER's can be fabricated out of        the thermoplastic materials commonly used to create fabrics, the        fabric itself could completely or partially comprise a DER. This        would eliminate the need to coat the fabric.    -   (6) Should one desire to electroplate a thermoformed article or        structure, DER's would represent an eminently suitable material        choice. DER's can be easily formulated using olefinic materials        which are often a preferred material for the thermoforming        process. Furthermore, DER's can be easily and inexpensively        extruded into the sheetlike structure necessary for the        thermoforming process.    -   (7) Should one desire to electroplate an extruded article or        structure, for example a sheet or film, DER's can be formulated        to possess the necessary melt strength advantageous for the        extrusion process.    -   (8) Should one desire to injection mold an article or structure        having thin walls, broad surface areas etc. a DER composition        comprising a high flow polymer can be chosen.    -   (9) Should one desire to vary adhesion between an        electrodeposited DER structure supported by a substrate the DER        material can be formulated to supply the required adhesive        characteristics to the substrate. For example, the polymer        chosen to fabricate a DER ink can be chosen to cooperate with an        “ink adhesion promoting” surface treatment such as a material        primer or corona treatment.

All polymer fabrication processes require specific resin processingcharacteristics for success. The ability to “custom formulate” DER's tocomply with these changing processing and end use requirements whilestill allowing facile, quality electroplating is a significant factor inthe teachings of the current invention.

Another important recognition regarding the suitability of DER's for theteachings of the current invention is the simplicity of theelectroplating process. Unlike many conventional electroplated plastics,DER's do not require a significant number of process steps prior toactual electroplating. This allows for simplified manufacturing andimproved process control. It also reduces the risk of crosscontamination such as solution dragout from one process bath beingtransported to another process bath. The simplified manufacturingprocess will also result in reduced manufacturing costs.

Another important recognition regarding the suitability of DER's for theteachings of the current invention is the wide variety of metals andalloys capable of being electrodeposited. Deposits may be chosen forspecific attributes. Examples may include copper or silver forconductivity and nickel or chromium for corrosion resistance, and tin ortin based alloys for solderability.

Yet another recognition of the benefit of DER's for the teachings of thecurrent invention is the ability they offer to selectively electroplatean article or structure. The articles of the current invention oftenconsist of metal patterns selectively positioned in conjunction withinsulating materials. Such selective positioning of metals is oftenexpensive and difficult. However, the attributes of the DER technologymake the technology eminently suitable for the production of suchselectively positioned metal structures. As will be shown in laterembodiments, it is often desired to electroplate a polymer orpolymer-based structure in a selective manner. DER's are eminentlysuitable for such selective electroplating.

Yet another recognition of the benefit of DER's for the teachings of thecurrent invention is the ability they offer to continuously electroplatean article or structure. As will be shown in later embodiments, it isoften desired to continuously electroplate articles. DER's are eminentlysuitable for such continuous electroplating. Furthermore, DER's allowfor selective electroplating in a continuous manner.

Yet another recognition of the benefit of DER's for the teachings of thecurrent invention is their ability to withstand the pre-treatments oftenrequired to prepare other materials for plating. For example, were a DERto be combined with a metal, the DER material would be resistant to manyof the pre-treatments such as cleaning which may be necessary toelectroplate the metal.

Yet another recognition of the benefit of DER's for the teachings of thecurrent invention is that the desired plated structure often requiresthe plating of long and/or broad surface areas. As discussed previously,the coverage rate accelerators included in DER formulations allow forsuch extended surfaces to be covered in a relatively rapid manner thusallowing one to consider the use of electroplating of conductivepolymers.

These and other attributes of DER's may contribute to successfularticles and processing of the instant invention. However, it isemphasized that the DER technology is but one of a number of alternativemetal deposition or positioning processes suitable to produce many ofthe embodiments of the instant invention. Other approaches, such asprinting of conductive resin formulations, metal spraying, etching metalfoils, stamping metal foils, laminating metal foils, positioning andaffixing metal patterns, electroless metal deposition, vacuum metalevaporation and sputtering, or electroplating onto various conductiveink patterns such as those comprising silver may be suitablealternatives. These choices will become clear in light of the teachingsto follow in the remaining specification, accompanying figures andclaims.

In order to eliminate ambiguity in terminology, for the presentinvention the following definitions are supplied:

While not precisely definable, for the purposes of this specification,electrically insulating materials may generally be characterized ashaving electrical resistivities greater than 10,000 ohm-cm. Also,electrically conductive materials may generally be characterized ashaving electrical resistivities less than 10,000 ohm-cm. A subset ofconductive materials, electrically resistive or semi-conductivematerials may generally be characterized as having electricalresistivities in the range of 0.001 ohm-cm to 10,000 ohm-cm. The term“electrically conductive polymer or resin” as used in the art and inthis specification and claims extends to materials of a very wide rangeof resitivities from about 0.00001 ohm-cm. to about 10,000 ohm-cm andhigher.

An “electroplateable material” is a material having suitable attributesthat allow it to be coated with a layer of electrodeposited material,either directly or following a preplating process.

A “metallizable material” is a material suitable to be coated with ametal deposited by any one or more of the available metallizing process,including chemical deposition, vacuum metallizing, sputtering, metalspraying, sintering and electrodeposition.

“Metal-based” refers to a material or structure having at least onemetallic property and comprising one or more components at least one ofwhich is a metal or metal-containing alloy.

“Alloy” refers to a substance composed of two or more intimately mixedmaterials.

“Group VIII metal-based” refers to a substance containing by weight 50%to 100% metal from Group VIII of the Periodic Table of Elements.

“metal-based foil” refers to a thin structure of metal or metal-basedmaterial that may maintain its integrity absent a supporting structure.Generally, metal of thickness greater than about 2 micrometers may havethis characteristic (i.e. 2 micrometers, 10 micrometers, 25 micrometers,100 micrometers, 250 micrometers).

A “film” refers to a thin material form that is not necessarily selfsupporting.

In this specification and claims, the terms “monolithic” or “monolithicstructure” are used as is common in industry to describe an object thatis seamless and made or formed into or from a single item.

A “continuous” process is one wherein a continuous form of a materialcomponent is supplied to the process. The material feed can becontinuous motion or repetitively intermittent, and the output is timedto remove product either by continuous motion or repetitivelyintermittent according to the rate of input.

A “roll-to-roll” process is one wherein a material component is fed tothe process from a roll of material and the output of the process isaccumulated in a roll form.

The “machine direction” is that direction in which material istransported through a process step.

The term “multiple” is used herein to mean “two or more”.

A “web” is a thin, flexible sheetlike material form often characterizedas continuous in a length direction.

“Sheetlike” characterized a structure having surface dimensions fargreater than the thickness dimension.

“Substantially planar” characterizes a surface structure which maycomprise minor variations in surface topography but from an overall andfunctional perspective can be considered flat.

The terms “upper” and “top” surfaces of structure refer to thosesurfaces of structure facing toward the light incident side of thestructure and are thus depicted in the drawing embodiments as facingupward.

The terms “lower” or “bottom” surface refer to surfaces facing away fromthe light incident side of the structure.

OBJECTS OF THE INVENTION

An object of the invention is to eliminate the deficiencies in the priorart methods of producing expansive area, interconnected photovoltaicarrays. A further object of the present invention is to provide improvedsubstrates to facilitate electrical interconnections among thin filmcells. A further object of the invention is to permit inexpensiveproduction of high efficiency thin film photovoltaic cells whilesimultaneously permitting the use of polymer based substrate materialsand associated processing to effectively interconnect those cells. Afurther object of the present invention is to provide improved processeswhereby expansive area, interconnected photovoltaic arrays can beeconomically mass produced.

Other objects and advantages will become apparent in light of thefollowing description taken in conjunction with the drawings andembodiments.

SUMMARY OF THE INVENTION

The current invention provides a solution to the stated need by firstindependently producing the active photovoltaic cell structure in a wayto maximize efficiency and performance. An embodiment of the inventioncontemplates deposition of thin film photovoltaic junctions on bulkmetal foil substrates which can be heat treated following deposition ina continuous fashion without deterioration of the metal supportstructure. In an embodiment of the invention the photovoltaic junctionwith its metal foil support can be produced in bulk using continuousroll-to-roll processing. The cell structure is subsequently combinedwith a unique interconnecting substrate to produce a desired expansiveinterconnected array or module of individual cells. In an embodiment ofthe invention, the unique interconnecting substrate may be producedusing continuous processing. In an embodiment of the invention,combining of individual cells with the interconnecting substrate isaccomplished using continuous or semi-continuous processing therebyavoiding the expensive and difficult batch assembly characteristic ofmany module assembly operations.

In an embodiment of invention the interconnection substrate structurecan comprise a wide selection of polymer-based materials since it doesnot have to endure high temperature exposure.

The interconnecting substrates of the current invention arecharacterized as having a substantially planar or sheetlike structure ofone or more units, each of said units comprising both electricallyconductive and non-conductive surface regions. In an embodiment,multiple photovoltaic cells overlay an individual unit ofinterconnecting substrate. In this embodiment, a conductive region ofthe substrate unit is electrically joined to the overlaying metal foilsubstrate of a first cell. The metal foil substrate of a second celloverlays and is attached to the non-conductive surface region of theunit. This positioning thereby insulates the metal foil substrate of thesecond cell from the conductive region of the unit. Series connection iscompleted between the first and second cells by establishing currentpaths between the top surface of the second cell and the conductivematerial of the unit. A number of options exist to achieve the currentpaths.

In an embodiment of the invention, the positioning of multiple cells ona unit of substrate may be accomplished using continuous orsemi-continuous processing.

In embodiments of the invention, photovoltaic cells can be combined withthe interconnecting substrate structures of the invention to achieveelectrical interconnections while minimizing the need to use expensiveand intricate material removal operations currently taught in the art toachieve series interconnections.

The interconnecting substrate structures of the current invention permitmaking electrical connections from the top of a cell to the bottomelectrode of an adjacent cell from above without the requirement toremove material to expose a top surface of the bottom electrode. Thisadvantage also eliminates the need to turn over strings of multiplecells during the interconnection process. Finally, the ability to makeboth these contacts from the top is more conducive to automated, highvolume production of integrated arrays.

BRIEF DESCRIPTION OF THE DRAWINGS

The various factors and details of the structures and manufacturingmethods of the present invention are hereinafter more fully set forthwith reference to the accompanying drawings wherein:

FIG. 1A is a top plan view of a prior art arrangement forinterconnecting multiple photovoltaic cells.

FIG. 1B is a bottom plan view of the prior art arrangement embodied inFIG. 1A.

FIG. 1C is a side view of the prior art arrangement embodied in FIGS. 1Aand 1B.

FIG. 2A embodies a step in the process of producing a prior artstructure.

FIG. 2B is a sectional view of a further step in a prior art process.

FIG. 2C is a sectional view of yet a further step in the prior artprocess.

FIG. 3 is a top plan view of a thin film photovoltaic structureincluding its support structure.

FIG. 3A is a top plan view of the article of FIG. 3 following anoptional processing step of subdividing the article of FIG. 3 into cellsof smaller dimension.

FIG. 4 is a sectional view taken substantially along the line 4-4 ofFIG. 3.

FIG. 4A is a sectional view taken substantially along the line 4A-4A ofFIG. 3A.

FIG. 4B is a simplified sectional depiction of the structure embodied inFIG. 4A.

FIG. 5 is an expanded sectional view showing a form of the structure ofsemiconductor 11 of FIGS. 4 and 4A.

FIG. 6 illustrates a possible process for producing the structure shownin FIGS. 3-5.

FIG. 7 is a sectional view illustrating the problems associated withmaking series connections among thin film photovoltaic cells shown inFIGS. 3-5.

FIG. 8 is a top plan view of an embodiment of a substrate structure forachieving series interconnections of thin film photovoltaic cells.

FIG. 9 is a sectional view taken substantially along the line 9-9 ofFIG. 8.

FIG. 9A is a sectional view of an alternate embodiment of a substratestructure for achieving series interconnections among thin filmphotovoltaic cells.

FIG. 9B is a sectional view of another embodiment of a substratestructure for achieving series interconnections among thin filmphotovoltaic cells.

FIG. 10 is a sectional view showing an alternate embodiment of asubstrate structure for achieving series interconnections of thin filmphotovoltaic cells.

FIG. 11 is a top plan view of an alternate embodiment of a substratestructure for achieving series interconnections of thin filmphotovoltaic cells.

FIG. 12 is a sectional view taken substantially along the line 12-12 ofFIG. 11.

FIG. 13 is a top plan view of another embodiment of a substratestructure for achieving series interconnections of thin filmphotovoltaic cells.

FIG. 14 is a sectional view taken substantially along the line 14-14 ofFIG. 13.

FIG. 15A is a side view depiction of a process for combining the foilsupported thin film photovoltaic structure of FIGS. 3 through 5 to aninterconnecting substrate structure.

FIG. 15B is a sectional view taken substantially along line 15B-15B ofFIG. 15A.

FIG. 16A is a top view of the structure resulting from the combinationprocess of FIGS. 15A and 15B and using the substrate structure of FIG.9.

FIG. 16B is a top view of the structure resulting from the combinationprocess of FIGS. 15A and 15B and using the substrate structure of FIG.10.

FIG. 16C is a top view of the structure resulting from the combinationprocess of FIGS. 15A and 15B and using the substrate structure of FIG.12.

FIG. 17A is a sectional view taken substantially along the lines 17A-17Aof FIG. 16A.

FIG. 17B is a sectional view taken substantially along the lines 17B-17Bof FIG. 16B.

FIG. 17C is a sectional view taken substantially along the lines 17C-17Cof FIG. 16C.

FIG. 17D is a sectional view similar to FIGS. 17A-17C illustrating anadditional embodiment of structure resulting from a combining processsuch as that embodied in FIGS. 15A and 15B employing the substratestructure of FIG. 9A.

FIG. 17E is a sectional view similar to FIGS. 17A-17D illustrating anadditional embodiment of structure resulting from the combinationprocess of FIGS. 15A and 15B employing the substrate structure of FIG.9B.

FIG. 17F is a sectional view similar to FIG. 17E employing a variationof the substrate structure of FIG. 9B.

FIG. 18 is a top plan view of the structure resulting from thecombination process of FIG. 15 and using the substrate structure ofFIGS. 13 and 14.

FIG. 19 is a sectional view taken substantially along the line 19-19 ofFIG. 18.

FIG. 20 is a top plan view of the structures of FIGS. 16A and 17A butfollowing an additional step in manufacture of the interconnected cells.

FIG. 21 is a sectional view taken substantially along the line 21-21 ofFIG. 20.

FIG. 22 is a top plan view of an embodiment of a completedinterconnected array.

FIG. 23 is a sectional view taken substantially along line 23-23 of FIG.22.

FIG. 24 is a sectional view similar to FIG. 23 embodying an alternatestructure for achieving an interconnected array.

FIG. 24A is an exploded view of the structure contained within thecircle K of FIG. 24.

FIG. 25 is a sectional view similar to FIG. 24 embodying anotheralternate structure for achieving an interconnected array.

FIG. 25A is an exploded view of the structure contained within thecircle L of FIG. 25.

FIG. 26 is a sectional view similar to FIGS. 24 and 25 embodying anotheralternate structure for achieving an interconnected array.

FIG. 26A is an exploded view of the structure contained within thecircle M of FIG. 26.

FIG. 27 is a sectional view similar to FIGS. 23-26 employing theinterconnect substrate structure and cell combination of FIG. 17F tofacilitate interconnection.

FIG. 27A is an exploded view of the structure contained within thecircle N of FIG. 27.

FIG. 28 is a sectional view similar to FIG. 17A but showing an alternateembodiment of the combined structure resulting from the combinationprocess of FIG. 15.

FIG. 29 is a sectional view similar to FIG. 17A but showing an alternateembodiment of the combined structure.

FIG. 30 is a sectional view of an alternate embodiment.

FIG. 31 is a sectional view of the embodiment of FIG. 29 after a furtherprocessing step.

FIG. 32 is a sectional view of another embodiment of an article in themanufacture of series interconnected arrays.

FIG. 33 is a top plan view of a structure suitable for achieving facileelectrical connections.

FIG. 34 combines a sectional view taken substantially from theperspective of lines 34-34 of FIG. 33 shown juxtaposed with anadditional article prior to combination.

DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. In the drawings, like reference numerals designate identical,equivalent or corresponding parts throughout several views and anadditional letter designation is characteristic of a particularembodiment.

Referring to FIGS. 3 and 4, an embodiment of a thin film photovoltaicstructure is generally indicated by numeral 1. It is noted here that“thin film” has become commonplace in the industry to designate certaintypes of semiconductor materials in photovoltaic applications. While thecharacterization “thin film” may be used to describe many of theembodiments of the instant invention, principles of the invention mayextend to photovoltaic devices not normally considered “thin film” suchas single crystal or polysilicon devices, as those skilled in the artwill readily appreciate. Structure 1 has a light-incident top surface 59and a bottom conductive surface 66. Structure 1 has a width X−1 andlength Y−1. It is contemplated that length Y−1 may be considerablygreater than width X−1 such that length Y−1 can generally be describedas “continuous” in the “Y” dimension or able to be processed in aroll-to-roll fashion in the “Y” direction. FIG. 4 shows that structure 1of the FIG. 3 embodiment comprises a thin film semiconductor structure11 supported by metal-based foil structure 12. Foil structure 12 has atop surface 65, bottom surface 66, and thickness “Z”. Metal-based foilstructure 12 may be of uniform composition or may comprise a multiplelayers. For example, foil structure 12 may comprise a base layer ofinexpensive and processable metal 13 with an additional metal-basedlayer 14 disposed between base layer 13 and semiconductor structure 11.The additional metal-based layer 14 may be chosen to ensure good ohmiccontact between the top surface 65 of foil structure 12 and photovoltaicsemiconductor structure 11. Bottom surface 66 of foil structure 12 maycomprise a material 75 chosen to achieve good electrical and mechanicaljoining characteristics as will be shown. Foil structure 12 may alsocomprise additional conductive layers such as a conductive polymericlayer. The thickness “Z” of foil structure 12 is often between 5micrometer and 250 micrometer (i.e. 5 micrometer, 10 micrometer, 25micrometer, 100 micrometer, 250 micrometer) although thicknesses outsidethis range may be functional in certain applications. A foil thicknessbetween 10 micrometer and 250 micrometer is often selected to provideadequate handling strength while still allowing flexibility forroll-to-roll processing, as further taught hereinafter. In theembodiment of FIGS. 3 and 4, foil structure 12 may also serve as a backelectrode for the cell structure and bottom surface 66 is electricallyconductive.

Should cell structure be produced having other forms of support, foilstructure 12 may be replaced by alternate conductive structure to form aback electrode. For example, crystalline silicon cells or thin filmcells supported by glass superstrates may be formed with conductive inksor pastes or very thin deposited metal layers as back electrodes.Normally, however, the back electrode will have an exposed portion tofacilitate connection.

In its simplest form, a photovoltaic structure combines an n-typesemiconductor with a p-type semiconductor to from a p-n junction. Mostoften a top surface electrode comprising an optically transparentconductive top layer such as a thin film of zinc or tin oxide isemployed to minimize resistive losses involved in current collection.The transparent conductive layer is often combined with a pattern oftraces formed of highly conductive material (not shown in FIG. 5) toform a composite top surface electrode. FIG. 5 illustrates an example ofa typical photovoltaic structure in section. In FIGS. 4 and 5 and otherselected figures, an arrow labeled “hv” is used to indicate the lightincident top surface of the structure. In FIG. 5, 15 represents a thinfilm of a p-type semiconductor, 16 a thin film of n-type semiconductorand 17 the resulting photovoltaic junction. A top electrode 18 completesthe typical photovoltaic structure. The top electrode normally comprisesa transparent conductive oxide (TCO) layer 18, sometimes referred to asa “window electrode”. The TCO is sometimes augmented with highlyelectrically conductive traces in the form of a grid (not shown in FIG.5. The exact nature of the photovoltaic semiconductor structure 11 doesnot form the subject matter of the present invention. For example, cellscan be multiple junction or single junction and comprise homo or heterojunctions. Semiconductor structure 11 may comprise any of the thin filmstructures known in the art, including but not limited to CIS, CIGS,CdTe, Cu2S, amorphous silicon, polymer based semiconductors and thelike. Structure 11 may also comprise organic solar cells such as dyesensitized cells. The method used to deposit the thin film semiconductormaterial onto the foil 12 may be selected from processes known in theart. These include vacuum deposition, chemical vapor deposition,physical vapor deposition, sputtering, printing, electroplating andelectrodes plating and the like. Such processes are often suitable forhigh volume, continuous roll-to-roll deposition of the semiconductormaterials onto the metal foil supporting substrate. Further,semiconductor structure 11 may also represent characteristically“non-thin film” cells such as those based on single crystal orpolycrystal silicon since many embodiments of the invention mayencompass such cells, as will be evident to those skilled in the art inlight of the teachings to follow.

In the following, photovoltaic cells having a metal based support foilwill be used to illustrate the embodiments and teachings of theinvention. However, those skilled in the art will recognize that many ofthe embodiments of the instant invention do not require the presence ofa “bulk” foil as represented in FIGS. 3 and 4. In many embodiments,other conductive substrate structures, such as conductive polymer films,metal meshes, vacuum, chemical or electrodeposited films and the like,as are known in the art may be suitable. Nevertheless, it is oftenadvantageous for the back electrode of the basic cell to have an exposedconductive back surface as will be clear in the teachings to follow.

FIG. 6 refers to a method of manufacture of the bulk thin filmphotovoltaic structures generally illustrated in FIGS. 3 and 4. In theFIG. 6 embodiment, a continuous form of self supporting metal-based foilstructure 12 is moved in the direction of its length Y through adeposition process, generally indicated as 19. Process 19 accomplishesdeposition of the active photovoltaic structure onto metal foil 12.Metal foil 12 is unwound from supply roll 20 a, passed throughdeposition process 19 and rewound onto takeup roll 20 b. Process 19 cancomprise any of the processes well-known in the art for depositing thinfilm photovoltaic structures. These processes include electroplating,vacuum evaporation and sputtering, chemical deposition, and printing ofnanoparticle ink precursors. Process 19 may also include treatments,such as heat treatments, intended to enhance photovoltaic cellperformance.

One readily realizes that the foil structure 12 employed in aroll-to-roll process such as embodied in FIG. 6 should have a thicknessand integrity appropriate for the continuous processing while retainingflexibility for roll accumulation. Generally, foils having thicknessgreater than about 3 to 4 micrometer (i.e. 10 micrometer, 25 micrometer,100 micrometer, 250 micrometer) may have this ability. Alternatively, insome cases the process depicted in FIG. 6 may be accomplished with metalfoil structures supported on a support structure such as a polymericfilm. The polymeric film may be a surrogate support and removed afterformation of the semiconductor layers.

Those skilled in the art will readily realize that the depositionprocess 19 of FIG. 6 may most efficiently produce photovoltaic structure1 having dimensions far greater than those suitable for individual cellsin an interconnected array. Thus, the photovoltaic structure 1 may besubdivided into cells 10 having dimensions X-10 and Y-10 as indicated inFIGS. 3A and 4A for further fabrication. Such subdivision may beaccomplished by well know methods of cutting and slitting. In FIG. 3A,width X-10 defines a first terminal edge 45 of cell 10 and a secondterminal edge 46 of cell 10. In one embodiment, for example, X-10 ofFIG. 3A may be from 0.20 inches to 12 inches and Y-10 of FIG. 3A may becharacterized as “continuous”. In other embodiments the final form ofcell 10 may be rectangular, such as 6 inch by 6 inch, 4 inch by 3 inchor 8 inch by 2 inch. In other embodiments, the photovoltaic structure 1of FIG. 3 may be subdivided in the “X” dimension only thereby retainingthe option of further processing in a “continuous” fashion in the “Y”direction. In the following, cells 10 in this (possibly subdivided) formhaving dimensions suitable for interconnection into a multi-cell arraymay be referred to as “cell stock” or simply as cells. “Cell stock” canbe characterized as being either continuous or discrete. In thisspecification and claims, the surface dimensions cells or cell stock aretaken to be the dimensions of the support metal foil. Such a definitionmay remove ambiguity should semiconductor be removed from edges ofcells. The thickness of cells or cell stock is the aggregate totalthickness of foil plus semiconductor plus TCO if present.

FIG. 4B is a simplified depiction of cell 10 shown in FIG. 4A. In orderto facilitate presentation of the aspects of the instant invention, thesimplified depiction of cell 10 shown in FIG. 4B will normally be used.

Referring now to FIG. 7, there are illustrated cells 10 as shown in FIG.4A. The cells have been positioned to achieve spatial positioning on thesupport substrate 21. Support structure 21 is by necessitynon-conductive at least in that distance indicated by numeral 70separating the adjacent cells 10. This insulating space prevents shortcircuiting from metal foil structure 12 of one cell to foil structure 12of an adjacent cell. In order to achieve series connection, electricalcommunication must be made from the top surface of window electrode 18to the foil structure 12 of an adjacent cell. This communication resultsin a net current flow in the direction of the arrow identified as “i” inFIG. 7. This net current flow direction is substantially in thedirection of width X-10 of photovoltaic cell 10. Electricalcommunication from top surface of window electrode 18 to the foilstructure 12 of an adjacent cell is shown in FIG. 7 as a metal wire 41.It is noted that foil structure 12 is normally relatively thin, on theorder of 0.001 cm to 0.025 cm. Therefore connecting to its edge asindicated in FIG. 7 would be impractical for inexpensive continuousproduction and is shown for illustration purposes only. Further,discrete electrical connections to the bottom of foil structure 12, assuggested in the “string and tab” arrangement depicted in FIGS. 1A-1C,is also inconvenient for high volume, rapid interconnection ofphotovoltaic cells since these connections to the bottom surface must bemade individually prior to final assembly of the interconnected cellsinto a fixed modular arrangement.

Referring now to FIGS. 8 and 9, one embodiment of the interconnectingsubstrate structures of the current invention is generally indicated by22. As depicted in the FIGS. 8 and 9 embodiments, unit of substrate hasa substantially planar upper surface having surface dimensions muchgreater than thickness dimension Z-23 and thus unit 22 can becharacterized as having a sheetlike form. Unit of substrate 22 compriseselectrically conductive material 23. Unit of substrate 22 also compriseselectrically insulating material 25. Material 25 normally comprises apolymeric material. However, other insulating materials such as wood orglass could serve the insulating function in some applications. Material25 has non-conductive top surface 8. Non-conductive top surface 8extends between a first terminal edge 24 and second terminal edge 27.Electrically conductive material 23 has a top side conductive surfaceportion 26 extending between a first terminal edge 29 and a secondterminal edge 30 of conductive top surface 26. Width X-23 defines firstand second terminal edges 29 and 30 respectively of conductive topsurface portion 26. Electrically conductive material 23 also has abottom surface 28, length Y-23 and thickness Z-23. Top conductivesurface portion 26 of conductive material 23 may be thought of as havingtop collector surface 47 and top contact surface 48 separated byimaginary insulating boundary 49.

An alternate embodiment of a discrete unit of substrate, indicated as 22a, is illustrated in FIG. 9A. In the FIG. 9A embodiment, theelectrically insulating material 25 is positioned to overlay a portionof electrically conductive material 23. One understands that insulatingmaterial 25 may advantageously exhibit adhesive characteristics.Alternatively, an adhesive medium (not shown) may be disposed betweeninsulating material 25 and conductive material 23. In this case, widthdimension X-23 extending between terminal edges 29 and 30 of theconductive top surface 26 is less than the full width of electricallyconductive material 23. The structure of substrate unit 22 a embodied inFIG. 9A may have certain manufacturing advantages compared with thestructure depicted in FIG. 9. It is clear that the relative extents ofthe conductive and non-conductive top surfaces of structure 22 a mayvary according to specific application.

A further embodiment of unit of substrate, indicated as 22 b, isillustrated in FIG. 9B. In the FIG. 9B embodiment, the electricallyinsulating material 25 is positioned on the bottom surface 28 ofelectrically conductive material 23.

It is important to note that the thickness variations depicted in thesectional views of FIGS. 9A and 9B result from drawing scale and thatsmall thickness variations of the actual article would not negatecharacterization of the articles as “sheetlike” or having substantiallyplanar surfaces.

In the embodiments of FIG. 9 through 9B, electrically conductivematerial 23 may comprise forms of most of the well know electricallyconductive materials such as metals or electrically conductive polymers.Typically, electrically conductive polymers exhibit bulk resistivityvalues of less than 10,000 ohm-cm. Resistivities less than 10,000 ohm-cmcan be readily achieved by compounding well-known conductive fillersinto a polymer matrix binder. Material 23 may alternatively comprise ametal foil or film.

Substrate units 22 through 22 b may be fabricated in a number ofdifferent ways. Electrically conductive material 23 can comprise anextruded film of electrically conductive polymer joined to a strip ofcompatible insulating polymer 25 at or near terminal edge 29 asillustrated in FIG. 9. The structures embodied in FIGS. 9A and 9B may beformed by applying non-conductive material 25 to the top or bottomsurface of conductive. material sheet 23 respectively.

Alternatively, the conductive material 23 may comprise a layer 23 aapplied to an insulating support structure 31 as illustrated in sectionin FIG. 10. For example, conductive material 23 a of FIG. 10 maycomprise a layer of electrically conductive polymer. In FIG. 10,electrically insulating regions 25 a are simply those portions ofinsulating support structure 31 not overlaid by conductive material 23a. It is seen that the embodiment of FIG. 10 consists of repetitiveunits, each unit comprising a conductive top surface region and anon-conductive top surface region.

It is contemplated that electrically conductive material 23, 23 a, etc.may comprise multiple materials. For example, a metal may beelectrodeposited onto an electrically conductive polymer for increasedconductivity and electrical joining characteristics. Metals such assilver, copper, nickel, zinc, tin and chromium can be electrodepositedquickly and inexpensively. The thicknesses of electrodeposited metalscan be closely controlled over a wide range, from for example 0.1 tohundreds of micrometers (i.e. 0.1 micrometer, 1 micrometer, 10micrometer, 100 micrometer) to hundreds of micrometers. Thus, anelectrodeposited metal may be produced as the electrical equivalent of abulk metal foil.

When considering electroplating, the use of a directly electroplateableresin (DER) may be particularly advantageous. DER's cover with metalrapidly by lateral growth of electrodeposit. In addition, selectivemetal coverage of a multi-material structure is readily achieved whenone of the materials is DER. For example, were conductive material 23shown in FIG. 9 to comprise a DER, exposing the FIG. 9 structure to anelectroplating bath would result in rapid metal electrodeposition ofconductive material 23 only while insulating material 25 would remainunplated. The fact that DER's are readily fabricated either as bulkcompositions or coatings qualifies DER's as being eminently suitable inthis application.

A further embodiment of interconnecting substrate is illustrated inFIGS. 11 and 12. In FIG. 11, electrically conductive material 23 bcomprises electrically conductive polymer coating or impregnated into afabric or web 32. A number of known techniques can be used to achievesuch coating or impregnation. Insulating joining region 25 b in FIG. 11is simply an uncoated portion of the web 32. Thus, the FIGS. 11 and 12embodiment consists of repetitive units, each unit comprising aconductive top surface region and a non-conductive surface region.Fabric or web 32 can be selected from a number of woven or non-wovenfabrics, including non-polymeric materials such as fiberglass.Alternatively, the material forming 23 b may comprise a fabric structureformed from a material which is itself conductive or capable offacilitating a subsequent metal deposition. Typical materials such as afabric of metal or DER fibrils or a catalyzed ABS may be appropriate. Inthis case optional subsequent metal deposition would produce a highlyconductive, monolithic surface to material 23 b.

Referring to the group of embodiments of interconnecting substratestructure of FIG. 9 though 12, they all have a length indicated as the“Y” dimension. It is contemplated in all cases that the length may bemuch greater than a width and the structures may be manufactured andfurther processed using continuous processing. Should the structures besuitably flexible, roll-to-roll processing is further contemplated.

Referring now to FIG. 13, an alternate embodiment for the substratestructures of the present invention is illustrated. In the FIG. 13embodiment, an insulating web or film 33 extends among and contributesto multiple individual units, generally designated by repeat structure34. In the FIG. 13 embodiment, electrically conductive material 35 ispositioned repetitively on sheetlike insulating web or film 33. At thestage of overall manufacture illustrated in FIG. 13, electricallyconductive material sheets 35 may simply comprise a metal foil. Usingconductive monolithic sheets such as a “bulk” metal foil may havecertain manufacturing advantages such as ease of preparation. It isreadily understood that the electrically conductive material sheets 35are analogous to and serve the same purpose as conductive materialsheets 23 of FIGS. 8 through 12. The electrically conducting materialsheets 35 normally will be attached to the insulating web or film 33with integrity required to maintain positioning and dimensional control.This attachment may be accomplished with an adhesive, indicated bymaterial 36 of FIG. 14.

Conductive material sheets 35 are shown in FIGS. 13 and 14 as havinglength Y-35, width X-35 and thickness Z-35. It is contemplated thatlength Y-35 may be considerably greater than width X-35 and length Y-35can generally be described as “continuous” or being able to be processedin roll-to-roll fashion. Width X-35 defines a first terminal edge 53 andsecond terminal edge 54 of conductive material sheet 35.

It is important to note that the thickness of the conductive materialsheets 35, Z-35 must be sufficient to allow for continuous lamination tothe insulating web 33 should such continuous lamination be employed. Abulk metal foil would normally be specified. More specifically, whenusing metal based foils for sheets 35, thickness between 2.0 micrometerand 0.025 cm. may normally be appropriate.

As with the substrate structures of FIGS. 8 through 12, it may behelpful to characterize top surface 50 of conductive material sheets 35as having a top collector surface 51 and a top contact surface 52separated by an imaginary barrier 49. Conductive material sheet 35 alsois characterized as having a bottom surface 80.

Yet another way to produce structure equivalent to that embodied inFIGS. 13 and 14 is to choose material 36 of FIG. 14 to be a materialwhich promotes metal deposition. This material would be deposited in adesired pattern. Subsequent processing then deposits a metal film overthe surface of material 36 in the pattern defined by material 36. Anexample of such a suitable material 36 to perform this function would bea catalytically seeded ABS, which would catalyze chemical deposition ofmetal, such as is well known in the art. Chemical deposition ofsufficient duration, or a combination of chemical deposition followed byelectrodeposition, would result in a metal deposit having appropriatefunctionality as a “bulk” metal foil 35 described above in conjunctionwith FIGS. 13 and 14.

It is important to realize that the relative dimensions of thestructures embodied in the sectional views of FIGS. 9, 9A, 9B, 10, 12,and 14 are not necessarily to scale. However, as is clear from theembodiments of FIGS. 9 through 14, it is anticipated that often thesestructures will have length and width dimensions (indicated by “Y” and“X” in FIGS. 8 through 14) far greater than the thickness dimension, andwill be substantially “planar” or “sheetlike” in structure. While minorthickness variations may occur over the extended surface of thestructures (as indicated for example in the sectional views ofembodiments shown in 9A, 9B, 10, 12, 14) the overall surface topographyof the structures is substantially “planar” or “sheetlike”. Also, thesevarious structures may often be characterized as flexible. A materialstructure is considered flexible if it deforms in response to theapplication of force yet returns to substantially its original shapewhen the force is removed. In many cases the length may far exceed thewidth such that the structures may be processed in a continuousroll-to-roll fashion in the length direction. Finally, obvious variantsof the materials of construction and structures described for thevarious embodiments of FIGS. 9, 9A, 9B, and 10 through 14 are consideredto be within the scope of the instant invention.

It is readily realized that the photovoltaic cell structure of FIGS. 3through 5 may be initially prepared separate and distinct from theinterconnecting substrate structures taught in FIGS. 8 through 14. Thisinitial separation allows elevated temperature processing of cellstructure, possibly in bulk and having expansive surfaces, whilepermitting design of unique polymer containing interconnect substratestructures. The polymer containing substrates can be made flexible andbe processed in continuous roll-to-roll fashion. In addition, the use ofinterconnecting substrates supplied separately and after manufacture ofcell structure permits facile cell interconnection as will be taught inthe following.

Referring now to FIGS. 15A and 15B, a process is shown for combining acontinuous metal-based foil supported thin film photovoltaic structureof FIGS. 3 through 5 with a continuous form of substrate structurestaught in FIGS. 8 through 14. In the FIGS. 15A and 15B embodiment'scontinuous lamination is shown as one means to achieve the combination.Continuous roll lamination employing nip rollers as depicted in FIG. 15Ahas certain manufacturing benefits. However, one will understand thatmany other methods such as vacuum lamination or simple “layup” may beused to achieve the combination and the invention is not limited to thespecific process embodiment of FIGS. 15A and 15B. In FIGS. 15A and 15B,photovoltaic cell structure as illustrated in FIGS. 3 through 5 isindicated by numeral 10. In this embodiment, cell structures 10 areshown to be in a “continuous” form in the machine direction. Substratestructures as taught in the FIGS. 8 through 14 are indicated by thenumeral 22. In this embodiment, substrate structures 22 are shown to besupplied in a “continuous” form in the machine direction. Numeral 42indicates an electrically conductive joining means such as anelectrically conductive adhesive intended to join electricallyconductive metal-based foil 12 of FIGS. 3 through 5 to electricallyconductive material 23 of FIGS. 8 through 12 or electrically conductivesheets 35 of FIGS. 13 and 14. It will be appreciated by those skilled inthe art that the conductive adhesive 42 shown in FIGS. 15A and 15B isone of but a number of appropriate conductive joining techniques whichwould maintain required ohmic communication. For example, it iscontemplated that methods such as application of a conductive resinprior to lamination, spot welding, soldering, joining with low melttemperature alloys, crimped mechanical contacts and mechanical surfacecontacts maintained with surface pressure would serve as alternatemethods to accomplish the electrically conductive joining illustrated asachieved in FIGS. 15A and 15B with a strip of conductive adhesive 42.Should material 23 itself include an adhesively active top surfaceportion, such as might be offered by an electrically conductiveadhesive, the separate feed 42 might be eliminated. These equivalentmethods can be generically referred to as conductive joining means. InFIG. 15B, the process of FIG. 15A is illustrated using the substrate ofFIGS. 8 and 9.

It has been found that a particularly attractive conductive joining maybe achieved through a technique described herein as a laminated contact.One structure involved in the laminated contact is a first portion ofconductive structure which is to be electrically joined to a secondconductive surface. The first portion comprises a conductive patternpositioned over a surface of a hot melt type of adhesive. A hot meltadhesive is one whose full adhesive affinity is activated by heating,normally to a temperature where the material softens or meltssufficiently for it to flow under simultaneously applied pressure. Manyvarious hot melt materials, such as ethylene vinyl acetate (EVA), arewell known in the art.

In the process of producing a laminated contact, the exposed surface ofa conductive material pattern positioned on the surface of a hot meltadhesive is brought into facing relationship with a second conductivesurface to which is electrically joining is intended. Heat and pressureare applied to soften the adhesive which then flows around edges orthrough openings in the conductive pattern to also contact andadhesively “grab” the exposed second surface portions adjacent theconductive pattern. When heat and pressure are removed, the adhesiveadjacent edges of the conductive pattern now firmly fix features ofconductive pattern in secure mechanical contact with the second surface.

The laminated contact is particularly suitable for the electricaljoining requirements of many aspects of the instant invention. Anembodiment of a starting structure to achieve laminated electricaljoining is presented in FIGS. 33 and 34. FIG. 33 shows a top plan viewof an article 110. Article 110 comprises a metal mesh 112 positioned onthe surface of hot melt adhesive 114. Numeral 122 indicates holesthrough the mesh. One will realize that many different patterns ofconductive material will be suitable for a laminated contact as taughthere, including comb-like patterns, serpentine traces, monolithic metalmesh patterns, etc.

FIG. 34 show a sectional view of article 110 juxtaposed in facingrelationship to a mating conductive surface to which electrical joiningis desired. In the embodiment, article 110 is seen to be a composite ofthe conductive material pattern positioned on a top surface of hot meltadhesive film 114. In the embodiment, an additional support film 116 isincluded for structural and process integrity, and possibly barrierproperties. Additional film 116 may be a polymer film of a material suchas polyethylene terephthalate, polypropylene, polycarbonate, etc.Article 110 can include additional layered materials (not shown) toachieve desired functional characteristics. Also depicted in FIG. 34 isarticle 118 having a bottom surface 120. Surface 120 may represent, forexample, the bottom surface 66 of solar cell structure 10.

In order to achieve the laminated contact, articles 110 and 118 arebrought together in the facing relationship depicted and heat andpressure are applied. The adhesive layer softens and flows to contactsurface 120. In the case of the FIG. 34 embodiment, flow occurs throughthe holes 122 in the mesh. Upon cooling and removal of the pressure, themetal mesh is held in secure and firm electrical contact with surface120.

Referring now to FIGS. 16 and 17, there is shown the result of thecombination process of FIGS. 15A and 15B using the substrate structureof FIGS. 8 through 12. FIGS. 16A and 17A correspond to the substratestructures of FIGS. 8 and 9. FIGS. 16B and 17B correspond to thesubstrate structure of FIG. 10. FIGS. 16C and 17C correspond to thesubstrate structures of FIGS. 11 and 12. FIG. 17D corresponds to thesubstrate structure of FIG. 9A. FIGS. 17E and 17F correspond to thesubstrate structure of FIG. 9B.

FIGS. 16A through 16C show that the cells 10 have been positioned withfirst terminal edge 45 of one cell being substantially parallel tosecond terminal edge 46 of an adjacent cell.

In the FIGS. 17A, 17B and 17C, electrically conductive joining means 42is shown as extending completely and contacting the entirety of thebottom electrode surface 66 of metal-based foil supported photovoltaiccells 10. Such broad contact surface may allow the use of a conductiveadhesive having a relatively high intrinsic resistivity, such as thosecontaining primarily carbon black or graphite fillers. This completesurface coverage is not a requirement however in cases where theconductive joining means joining surface 66 with surface 26 is highlyconductive. Metal foil structure 12 is normally highly conductive andable to distribute current over the expansive width X-10 with minimalresistance losses. For example, the structure of FIG. 28 shows anembodiment wherein electrical communication is achieved between aconductive material sheet 23 of FIGS. 8 and 9 and bottom surface 66 offoil structure 12 through a narrow bead of a highly conductive joiningmeans 61. Examples of such a highly conductive joining means would be ametal based solder or a silver filled epoxy. An additional joining means44 may be used to ensure spatial positioning and dimensional support forthis form of structure. Joining means 44 may comprise an adhesive andthe adhesive need not be electrically conductive.

In FIG. 17D discrete units of substrate structure 22 a are joinedthrough cells 10. In addition an underlying insulating supportingmaterial (not shown in FIG. 17D) may be used to facilitate spatialpositioning of the multiple cells. In FIG. 17D, it is seen that thebottom surface 66 of an individual cell is in electrical communicationwith the conductive top surface 26 of conductive material 23 throughconductive joining means 42 and is also attached to the nonconductiveportion 25 of an adjacent unit of substrate. Conductive joining means 42may comprise for example an electrically conductive adhesive.Electrically conductive joining means 42 is shown in FIG. 17D to extendcompletely over the bottom surface 66 of cells 10. This completecoverage is not required, as explained above.

In FIG. 17E, discrete units of substrate structure 22 b are joinedthrough cells 10. In FIG. 17F, multiple units of substrate structure 22b are joined in an overlapping fashion as embodied in the FIG. 17F. Onewill readily understand that, while the structural variations depictedin FIGS. 17A through 17F employ the substrate structures embodied inFIGS. 9 through 9B, structures similar or equivalent to those of FIGS.17A through 17F could be prepared using the starting substratestructures of FIGS. 10 through 14.

In the FIGS. 17A, 17B and 17C, the conductive materials 23, 23 a and 23b are shown to be slightly greater in width X-23 than the width of foilX-10. As is shown in FIG. 29, this is not a requirement for satisfactorycompletion of the series connected arrays. FIG. 29 is a sectional viewof a form of the substrate structures of FIGS. 8 and 9 combined by theprocess of FIG. 15A to the photovoltaic structures of FIGS. 3 through 5.In FIG. 29, width X-10 is greater than width X-23. Electricalcommunication is achieved through conductive joining means 42 andadditional joining means 44 to achieve dimensional stability may beemployed. A common feature of the embodiments of the current inventionshown in FIGS. 17, 28, 29 and 31 is that the conductive material (23 or35) of a substrate unit be electrically joined to the bottom electrodeof a first cell 10 and also extend outward beyond a terminal edge (45 or46) of that first cell. In this way individual cells can be positionedto overlay the substrate units using convenient processing such aslaminating. The extension of the conductive material (23 or 35) beyond aterminal edge of the first cell essentially extends the bottom electrodeof the first cell such that it is accessible from above. The conductivematerials 23 or 35 of the substrate units are spaced apart from and donot actually extend to the top electrode of an adjacent cell. However,the extending material provides a convenient structure from which toform conductive paths to the top electrode of an adjacent cell, as willbe seen.

In FIG. 29, insulating material 25 is shown as extending continuouslyfrom second terminal edge 30 of one conductive surface 26 to the firstterminal edge 29 of an adjacent conductive surface. As shown in FIG. 32,this is not necessary. In FIG. 32, metal foil supported photovoltaiccell 10 is attached to a first conductive surface 26 throughelectrically conductive joining means 42 and also to insulating region25 of an adjacent substrate structure through additional joining means44. Additional joining means 44 may comprise for example anon-conductive adhesive. Thus, the substrate structure 22 may bediscrete. In the embodiment of FIG. 32, the foil based photovoltaicstructure 10 is of sufficient strength to maintain proper spacedrelationships and positioning among cells. It is understood thatadditional support (not shown in FIG. 32) may be employed.

Referring now to FIGS. 18 and 19, there is shown an alternate structureresulting from the combination process of FIG. 15A as applied to thephotovoltaic cells of FIGS. 3 through 5 and the substrate structure ofFIGS. 13 and 14. The first terminal edge 53 of conductive materialsheets 35 supported by insulating web 33 are slightly offset from thefirst terminal edge 45 of photovoltaic cells 10. This offset allows aportion of top surface 50 of conductive material sheet 35 to beavailable for connecting to an electrode of an adjacent cell. Electricaland mechanical joining of conductive material sheets 35 with bottomsurface 66 of metal-based foil structure 12 is shown in FIG. 19 as beingachieved with conductive joining means 42 as in previous embodiments. Asin previous embodiments it is contemplated that this electrical andmechanical joining can be accomplished by means such as conductiveadhesives, soldering, joining with compatible low melting point alloys,spot welding, mechanical crimping, and mechanical pressure contacts.

It should also be observed that alternate process sequences may be usedto produce structures equivalent to those shown in FIGS. 16 through 19,28, 29 and 32. For example, a structure equivalent to that of FIGS. 18and 19 can also be achieved by first joining photovoltaic cells 10 andconductive material sheets 35 with suitable electrically conductivejoining means 42 to give the structure shown in FIG. 30 and laminatingthese strips to an insulating web or film 33. An example of such anequivalent structure is shown in FIG. 31, wherein the laminates of FIG.30 have been adhered to insulating web 33 in defined repeat positionswith adhesive means 57 and 44. As mentioned above and as shown in FIGS.30 and 31, conductive material sheets 35 do not have to contact thewhole of the bottom surface 66 of photovoltaic cell 10. In addition,insulating web 33 need not be continuous among all the cells.

Referring now to FIGS. 20 through 23, there is shown one method offorming the final interconnected array when employing the substratestructures embodied in FIGS. 8 and 9. In FIGS. 20 and 21, insulatingmaterials 56 and 60 have been applied to the first and second terminaledges 45 and 46 respectively of photovoltaic cells 10. While thesematerials 56 and 60 are shown as applied to the structure of FIG. 17A,it is understood that appropriate insulating material are alsoenvisioned as a subsequent manufacturing step for the structures of17B-17F, 19, 28, 29, 31, and 32. The purpose of the insulating materialsis to protect the edge of the photovoltaic cells from environmental andelectrical deterioration. In addition, the insulating materials may helpprevent electrical shorting when interconnections to be made amongadjacent cells.

It is noted that the application of insulating material 56 to firstterminal edge 45 of photovoltaic cells 10 effectively divides the topconductive surfaces 26 and 50 of conductive materials 23 and 35respectively into two regions. The first region (region 48 of surface 26or region 52 of surface 50) can be considered as a contact region forseries interconnects among adjacent cells. The second region (region 47of surface 26 or region 51 of surface 50) can be considered as thecontact or collector surface for interconnecting the substrate to thebottom surface 66 of photovoltaic cells 10.

In the embodiment of FIGS. 22 and 23, grid fingers 58 of a highlyelectrically conductive material are deposited in the form of fingers toharvest current from the top surface 59 of the photovoltaic cell 10.Conductive extensions 62 convey the harvested current to the contactregions 48 or 52 associated with an adjacent cell. It is contemplatedthat the fingers can be deposited by any of a number of processes todeposit metal containing or metal-based foils or films, including maskedvacuum deposition, printing of conductive inks, electrodeposition orcombinations thereof. The grid fingers are not considered to be a partof the substrate structure since they do not contribute to supportingand spatial positioning of the cells. They serve only to harvest currentfrom the top surface 59 of the cell. The conductive extensions 62 may beapplied simultaneously with the fingers or in a separate operation. Theextensions 62 may be applied using a number of processes to depositmetal containing or metal-based films identified above. Alternatively,the extensions may comprise a separately formed article such as a stripof bulk metal foil or mesh. In the embodiment of FIGS. 22 and 23, thedirection of net current flow through the interconnected arrayillustrated is indicated by the arrow identified as “i”, which directionis substantially parallel to width X-23 of electrically conductivesurface portion 26 of unit of substrate 22.

Referring now to FIG. 24 and the exploded view of FIG. 24A, there areembodied alternate structures for the final interconnected array whenemploying the substrate structure as embodied in FIG. 9A. In FIG. 24,there is embodied multiple photovoltaic cells 10 positioned oninterconnecting substrate units 22 a as in FIG. 17D. FIG. 24A is anexploded view of the structure contained within the circle K of FIG. 24.A space identified as “P-24” separates individual cells. In addition,insulating materials 56 and 60 have been deposited over the terminaledges 45 and 46 of the individual cells. A conductive ink pattern formsa grid pattern of fingers 58 positioned on the top surface of the cell.Conductive extensions, electrically joined to the fingers 58 andidentified by numeral 62, traverse over insulating material 60 and tothe conductive top surface 26 of conductive material sheets 23. Theconductive extensions 62 may be applied as described for the embodimentof FIGS. 22 and 23. Extensions 62 need not be the same material asfingers 58 nor need they be applied at the same time as fingers 58.Extensions 62 contact surface 26 using suitable conductive joining means(not shown) or through simple mechanical surface contact. In the FIGS.24 and 24A embodiments, conductive material sheets 23 furthercommunicate with conductive bottom surface 66 of an adjacent cellthrough electrically conductive joining means 42.

Referring now to FIG. 25 and the exploded view of FIG. 25A there isembodied another interconnected structure employing the substrate unitsof FIG. 9A. FIG. 25A is an exploded view of the structure containedwithin the circle L of FIG. 25. In FIGS. 25 and 25A there is embodiedmultiple photovoltaic cells positioned on units of interconnectingsubstrate 22 a as in FIG. 17D. In the FIGS. 25 and 25A embodiment,conductive vias 72 establish communication between the top surface 59 ofa cell 10 and the conductive material 23 of a unit of substrate 22 a.Conductive material 103 fills the vias and makes electrical connectionbetween the top surface 59 of cell 10 and conductive material 23.Conductive material 103 may comprise, for example, an electricallyconductive resin, a metal plug or rivet or staple. Conductive materialsheet 23 further communicates with conductive bottom surface 66 of anadjacent cell through electrically conductive joining means 42. Thesidewalls of the via are insulated by material 104. The insulatingmaterial 104 prevents contact of the conductive material 103 traversingthe via with the foil structure 12 of the cell through which the viaextends. FIGS. 25 and 25A also shows optional grid fingers 58 extendingfrom the conductive material of the vias over the top surface 59 ofcells 10.

In the embodiment of FIGS. 25 and 25A, individual cells are separated bya gap, identified by “P-25”. This gap may be very small. This structuralaspect may be important where space is of concern in that the amount ofilluminated surface lost through interconnecting is reduced compared toalternate arrangements.

Using conductive vias to achieve electrical communication between a celltop surface and a remote conductive material is known in the art. Seefor example Yoshida et al, U.S. Pat. No. 5,421,908, the entire contentsof which are herein incorporated by reference. However, the Yoshidastructure was essentially a monolithically integrated structurecomprising thin conductive materials of limited current carryingcapacity. In addition, a polymeric substrate was required to be presentduring initial cell manufacture in order to achieve the finalinterconnections. These factors and others significantly limited theYoshida teachings.

One readily notes that the extensions 62 of the FIGS. 23 and 24embodiments and vias 72 of FIG. 25 perform substantially the samefunction, that being to establish electrical communication between thetop cell surface and the conductive material of sheet 23 of substrateunit 22 a.

FIGS. 26 and 26A embody yet another structure for the finalinterconnected array employing the arrangement of FIG. 17D. FIG. 26A isan exploded view of the structure contained within the circle M of FIG.26. In FIG. 26, insulating materials 60 and 56 protect edges of thecells. Also shown in FIGS. 26 and 26A is metal foil or metal containingmesh straps 73 extending from the conductive top surface of a first cellto the conductive material 23 of a unit of interconnecting substrate22A. The “conductive joining means” connecting the strap to theconductive surfaces is not shown in the drawing but may be any of thenumber of conductive joining means previously identified. As shown inthe FIG. 26 embodiment, such straps need not extend to the baseelectrode of one of the cells as is the case for the prior artarrangement embodied in FIG. 1. This facilitates assembly because astring of cells need not be “turned over” to make connection to thebottom electrode of an adjacent cell. Nor must any semiconductormaterial be removed to accomplish electrical joining to the bottom cellelectrodes. Since there are a myriad of material and structural optionsto form the conductive surface region 26 of the interconnectingsubstrate unit of the instant invention, many different electricaljoining techniques are available. Finally, the interconnecting substrateallows very high surface conductivity, thereby allowing currenttransport over an expansive surface of a back electrode whileaccomplishing secure positioning of the cells. This latter advantagepermits facile and secure handling of multiple interconnected cellsduring final packaging of the multi-cell interconnected array.

Referring now to FIG. 27, a completed interconnected array is embodiedusing the substrate/cell arrangement embodied in FIG. 17F. FIG. 27A isan exploded view of the structure contained within the circle N of FIG.27. In FIGS. 27 and 27A, electrical traces or “fingers” 58 positionedover the cell surface lead to a conductive extension 62. The extension62 may be as described above in the description of FIGS. 24 and 24A. Theextension 62 is further electrically joined to the conductive material23 of a substrate unit associated with an adjacent cell. The FIG. 27arrangement allows insulating material 25 associated with an individualsubstrate unit to also function as a protection for a terminal edge ofthe abutting cell.

One notes that in the interconnected cell embodiments of FIGS. 22through 27, one notes that the conductive material 23 of a unit ofinterconnecting substrate extends outside a peripheral edge of the cellwhose bottom surface 66 is electrically joined to material 23 of theparticular unit. In this way an upward facing conductive surface ofconductive material 23 is accessible for electrical connection toadditional conductive material contributing to a conductive pathextending to the top electrode of another adjacent cell. This conditiongreatly facilitates making the final series connections in an efficient,high speed and automated process.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications,alternatives and equivalents may be included without departing from thespirit and scope of the inventions, as those skilled in the art willreadily understand. Such modifications, alternatives and equivalents areconsidered to be within the purview and scope of the invention andappended claims.

1. An article combining a first photovoltaic cell and a unit ofinterconnection substrate designed to promote facile series electricaland mechanical assembly of a multiple of said articles, said firstphotovoltaic cell having an upwardly facing top surface electrodecomprising a transparent conductive material, said cell furthercomprising thin film semiconductor material supported on an upwardlyfacing surface of a metal based cell foil, said metal based cell foilalso forming a conductive bottom surface electrode and being selfsupporting, said unit of interconnection substrate having a sheetlikeform with a substantially planar upwardly facing surface and comprisingconductive and non-conductive materials in addition to those associatedwith said cell structure, said article characterized by havingoverlapping portions of said first cell and the unit such that saidfirst cell portion overlays an upwardly facing surface of a firstportion of said additional conductive material of said unit and a secondportion of said additional conductive material extends outside aterminal edge of said cell and further that a portion of said additionalnon-conductive material forms an insulating barrier positioned betweensaid first portion of said additional conductive material and said metalbased cell foil, such that said additional conductive material does nothave ohmic electrical communication with said cell foil of said firstcell.
 2. The article of claim 1 wherein one or more ohmic conductorselectrically connect said upwardly facing top cell surface electrode andsaid first portion of the additional conductive material of the unit. 3.The article of claim 1 wherein one or more ohmic conductors electricallyconnect said upwardly facing top cell surface electrode and said secondportion of the additional conductive material of the unit.
 4. Thearticle of claim 2 wherein one or more ohmic conductors comprise anelectrically conductive polymeric resin.
 5. The article of claim 3wherein one or more ohmic conductors comprise an electrically conductivepolymeric resin.
 6. The article of claim 1 wherein said second extendingsecond portion of conductive material of said unit has an upwardlyfacing surface suitable for establishing facile electrical connection toan electrode of another photovoltaic cell.
 7. The article of claim 1wherein said extending second portion of conductive material of saidunit presents an electrically conductive upper surface suitable forelectrical connection to an electrode of a second cell.
 8. The articleof claim 1 wherein said conductive bottom surface of said metal basedcell foil of said first cell presents an electrically conductive bottomsurface suitable for electrical connection to an electrode of a secondcell.
 9. The article of claim 1 wherein said additional conductivematerial of said unit has a bottom surface that is at least partiallyexposed.
 10. The article of claim 1 wherein said metal based cell foilhas properties allowing a roll-to-roll manufacturing step in theproduction of said cells.
 11. The article of claim 1 wherein said metalbased cell foil has a thickness greater than about 10 micrometers. 12.The article of claim 1 wherein said metal based cell foil comprises astructure of multiple metal-based layers.
 13. The article of claim 1wherein a portion of said additional non-conductive material of saidunit is positioned to overlay an upper surface of a portion of saidadditional conductive material of said unit.
 14. The article of claim 1wherein said additional conductive material of said unit comprises anelectrodeposit.
 15. The article of claim 1 wherein said additionalconductive material of said unit comprises a second metal based foil.16. The article of claim 15 wherein said second metal based foil has athickness between 2 micrometer and 250 micrometer.
 17. The article ofclaim 1 wherein said additional conductive material of said unitcomprises an electrically conductive polymeric resin.
 18. The article ofclaim 15 wherein said second metal based foil has properties suitable toallow continuous lamination.
 19. The article of claim 1 wherein saidadditional non-conductive material of said unit comprises a materialhaving adhesive affinity for the conductive bottom surface of a saidcell.
 20. The article of claim 1 wherein said additional non-conductivematerial of said unit comprises a material having adhesive affinity forthe additional conductive material of the unit.
 21. The article of claim1 wherein a multiple of said interconnection units are joined togetherin a repetitive pattern.
 22. The article of claim 1 further comprising asecond photovoltaic cell, said second photovoltaic cell having anupwardly facing top surface electrode comprising a transparentconductive material, said second cell further comprising thin filmsemiconductor material supported on an upwardly facing surface of ametal based cell foil, said metal based cell foil also forming aconductive bottom surface electrode and being self supporting, saidsecond photovoltaic cell having its metal based cell foil in electricalohmic communication with said second portion of said additionalconductive material.
 23. The article of claim 22 wherein said electricalohmic communication is achieved using materials chosen from the group ofelectrically conductive polymers, and solders.
 24. The article of claim22 wherein said electrical ohmic communication is achieved using ajoining technique chosen from the group welding, crimped mechanicalcontacts, and laminated contacts.